MAC protocol employing multiple data rates

ABSTRACT

Method and apparatus for combining high data rate traffic and low data rate traffic on a common transmission medium while maximizing efficient use of available spectrum. Since spectrum is an economically valuable resource and transport of data generates revenue, the present invention directly leads to more profitable network operation. The disclosed systems are applicable to both wired and wireless transmission media. In one embodiment, a bandwidth reservation scheme provides that data rate may be varied so that when a particular data communication device is allocated a frame, it is also assigned a data rate for use in that frame. Because bandwidth usage varies with data rate, the division of available spectrum into channels for use by individual data communication devices may also vary among frames.

STATEMENT OF RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 10/202,496 entitled “MAC PROTOCOL EMPLOYING MULTIPLE DATARATES,” filed on Jul. 24, 2002, which was a continuation of U.S. patentapplication Ser. No. 09/097,305 entitled “MAC PROTOCOL EMPLOYINGMULTIPLE SYMBOL RATES,” filed Jun. 12, 1998, now U.S. Pat. No.6,463,096, both of which are incorporated herein in their entirety forall purposes.

BACKGROUND OF THE INVENTION

The present invention relates to digital communication and moreparticularly to protocols for communicating data originating fromsources having disparate data rates over a shared medium.

Trends in digital communication point toward a common transmissionmedium providing both high data rate services such as digital video andlow data rate services such as voice. Internet access is inherently amixed service. Upstream requests for information typically includeminimal data while downstream traffic may include graphics or even livevideo.

Specific examples of such a common transmission medium include awireless local loop (WLL) that substitutes for the local telephone loopand provides additional high data rate services such as video andInternet access. Another example is a CATV network that has been updatedto provide high data rate services and voice service.

A key objective is maximizing efficiency in use of bandwidth. Theavailable bandwidth is shared among multiple data communication devices.When a data communication device is allocated all or part of theavailable bandwidth, it should make efficient use of its allocation.Depending on the protocols and modulation systems used, a certainpercentage of the data is devoted to network operation rather thancustomer service. This is referred to as overhead. Consider a networkwhere packets of information are communicated in successive frames and:

d_(p)=Payload data (bits)—the number of payload bits contained in aframe,

r=Data rate (bits/sec), proportional to spectrum used (Hz). Data raterefers to the rate at which information is communicated through thewireless medium. Information rate roughly represents the rate ofgeneration of payload data.

t_(f)=Frame time (sec)—the duration of the smallest unit of time thatmay be allocated to a data communication device for transmission on theshared medium. Note that a packet of like data, such as voice or data,may be transmitted in a single frame or may be divided among manyframes.

t_(g)=Overhead time (sec), including guard time, training, andsynchronization that is required for each frame.

The system efficiency associated with the overhead given by t_(g) is${eff} = {{\frac{d_{p}}{r\left( {t_{g} + t_{f}} \right)} \cdot {This}}\quad{value}\quad{of}\quad{efficiency}\quad{reaches}\quad 100\quad\%{\quad\quad}{when}\quad{the}\quad{overhead}}$time is zero and the frame time equals the payload data divided by thedata rate (when the frame time is exactly the time required to transmitthe payload data at the transmission rate).

The network designer is left free to vary frame time to maximizeefficiency. However, it is difficult to reconcile the needs of differenttraffic types. Consider choosing one frame time to accommodate both lowinformation rate voice traffic and high information rate data traffic.Due to transmission latency requirements, voice traffic requiresfrequent frame transmissions to reduce latency. Hence, voice requires ashort frame time. Furthermore, the amount of data to be sent in theseframes is small since voice is low information rate. If long frames aresent, voice traffic is insufficient to fill each frame, resulting inwasted bandwidth. However, sending small frames incurs a different typeof bandwidth loss. The fixed overhead associated with each framesubstantially reduces spectral efficiency. This becomes particularlysignificant for high information rate traffic, where data must bedivided over many frames instead of being efficiently transmitted inlong frames. This conflict can be described in an example.

Consider choosing a frame time to efficiently transmit both a 64-bytevoice packet and a 1000-byte data packet. Assume an overhead time of 3us (t_(g)=3 us), a data rate of 30 Mbits/sec, and two candidate frametimes of 17 us and 267 us. For a frame time of 17 us, the efficiency fora 64-byte packet of data is,${eff}_{64} = {\frac{d_{p}}{r\left( {t_{g} + t_{f}} \right)} = {\frac{512}{30 \times 10^{6}\left( {\left( {3 + 17} \right) \times 10^{- 6}} \right)} = {\frac{17}{3 + 17} = {85\quad{\%.}}}}}$

Since the frame time is exactly the amount of time required to transmit64 bytes at a 30 Mbit/sec rate, this is the maximum efficiency at thisdata rate. A 1000-byte packet would be spread among 64-byte transmissionopportunities corresponding to individual frames. Hence the efficiencyfor a 1000 byte packet is approximately the same as for the 64-bytepacket. (To be precise, the efficiency is slightly less than 85% sincethe final frame is not fully utilized.)

Increasing the frame time can increase this efficiency by reducing theoverhead. For example, a frame time of 267 us results in close to 99%efficiency for a 1000 byte packet,${eff}_{1000} = {\frac{d_{p}}{r\left( {t_{g} + t_{f}} \right)} = {\frac{8000}{30 \times 10^{6}\left( {\left( {3 + 267} \right) \times 10^{- 6}} \right)} = {\frac{267}{3 + 267} = {99\quad{\%.}}}}}$

Unfortunately, this large frame time causes severe inefficiency for the64-byte packet because a large portion of the frame is left unutilized.Here it is assumed that because of latency requirements, it is notfeasible to collect multiple 64-byte packets to fill a frame. Forexample, it would take a 64 kbps voice source over 125 ms to fill a1000-byte frame, which results in intolerable latency. Allowing 8 ms oflatency for the collection of one 64-byte packet, the long frame capableof supporting 1000 bytes which carries one 64-byte packet has very poorefficiency:${eff}_{64} = {\frac{d_{p}}{r\left( {t_{g} + t_{f}} \right)} = {\frac{512}{30 \times 10^{6}\left( {\left( {3 + 267} \right) \times 10^{- 6}} \right)} = {\frac{17}{3 + 267} = {6\quad{\%.}}}}}$

No single choice of frame time leads to efficient use of the spectrumfor both high data rate and low data rate traffic.

SUMMARY OF THE INVENTION

The present invention provides methods and apparatus for combining highdata rate traffic and low data rate traffic on a common transmissionmedium while maximizing efficient use of available spectrum. Sincespectrum is an economically valuable resource and transport of datagenerates revenue, the present invention directly leads to moreprofitable network operation. The systems and methods provided by thepresent invention are applicable to both wired and wireless transmissionmedia. In one embodiment, a bandwidth reservation scheme provides thatdata rate may be varied so that when a particular data communicationdevice is allocated a frame, it is also assigned a data rate for use inthat frame. Because bandwidth usage scales with data rate, individualdata communication devices will be assigned to possibly differentspectrum bandwidth on a frame-by-frame basis.

A first aspect of the present invention provides a method for allocatingaccess to a common transmission medium among a plurality of datacommunication devices. The method includes steps of: assigning atransmission frame to a particular data communication device, assigninga data rate for the particular data communication device to employ inthe transmission frame, and transmitting the transmission frameassignment and the data rate assignment to the particular datacommunication device.

A second aspect of the present invention provides an alternative methodfor allocating access to a common transmission medium among a pluralityof data communication devices. The method includes steps of: receivingaccess request messages from requesting data communication devices at ahub, the access request messages requesting access to the commontransmission medium, in response to the access request messages, at thehub, allocating access to the common transmission medium in both thefrequency and time domain among the requesting data communicationdevices, and thereafter transmitting from the hub to the requestingaccess devices, instructions for each requesting access device totransmit at particular times, and at particular data rates chosenaccording to the allocating step.

A third aspect of the present invention provides a digital communicationnetwork including a plurality of data communications devicestransmitting via a common transmission medium, and a hub receivingsignals from the data communications devices via the common transmissionmedium. The hub includes: a bandwidth manager that receives accessrequest messages from requesting data communication devices, the accessrequest messages requesting access to the common transmission medium,and that allocates access to the common transmission medium in both thefrequency and time domain among the requesting data communicationdevices. The hub further includes a link supervisor that transmits fromthe hub to the requesting access devices, instructions for eachrequesting access device to transmit at particular, and at particulardata rates chosen in accordance with allocations by the bandwidthmanager.

A fourth aspect of the present invention provides a hub. The hubincludes: a receiver that receives signals from the data communicationsdevices via the common transmission medium, a bandwidth manager thatreceives access request messages from requesting data communicationdevices, the access request messages requesting access to the commontransmission medium, and that allocates access to the commontransmission medium in both the frequency and time domain among therequesting data communication devices. The hub further includes a linksupervisor that transmits from the hub to the requesting access devices,instructions for each requesting access device to transmit at particulartimes, and at particular data rates chosen in accordance withallocations by the bandwidth manager.

A fifth aspect of the present invention provides a data communicationsdevice for use in a network. The data communications device includes abandwidth manager that transmits requests for access to a commontransmission medium to a hub. The data communications device furtherincludes a link supervisor that receives medium access instructions fromthe hub, the medium access instructions specifying data rate,transmission time, and transmission frequency for transmissions to thedata communications device, and that controls transmission ofinformation via the common transmission medium in accordance with thespecified data rate, transmission time, and transmission frequency.

A further understanding of the nature and advantages of the inventionsherein may be realized by reference to the remaining portions of thespecification and the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a representative communications network suitable forimplementing one embodiment of the present invention.

FIG. 2 depicts a hub for the network of FIG. 1 according to oneembodiment of the present invention.

FIG. 3 depicts a data communications device in the network of FIG. 1according to one embodiment of the present invention.

FIG. 4A depicts frame assignments in the time domain according to oneembodiment of the present invention.

FIG. 4B depicts channel assignments in the frequency domain in arepresentative frame according to one embodiment of the presentinvention.

FIG. 5 depicts a hub radio system according to one embodiment of thepresent invention.

FIG. 6 depicts a data communications device radio system according toone embodiment of the present invention.

DESCRIPTION OF SPECIFIC EMBODIMENTS

FIG. 1 depicts a representative communications network 100 suitable forimplementing one embodiment of the present invention. Althoughcommunications network 100 is depicted as a wireless network, it will beunderstood that the present invention is applicable to both wired andwireless networks. A hub 102 acts as a central access point for network100. Hub 102 may communicate with a plurality of CPEs 104 (customerpremise equipment) which represent data communication. devices. Abackbone class IP router 106 may interconnect hub 102 and the Internet108.

In one embodiment, network 100 implements a wireless local loop thatprovides local telephone services as well as high data rate services.Antennas 110 are used to couple hub 102 and CPEs 104 to the commonwireless transmission medium. Spectrum is allocated for the use ofnetwork 100. In a preferred embodiment, downstream communications (i.e.,communications from hub 102 to CPEs 104) are frequency domain duplexedwith upstream communications (from CPEs 104 to hub 102). However,downstream and upstream traffic may also be duplexed in the time domain.

In another embodiment, network 100 is a cable television system. Hub 102represents the cable head-end and CPEs 104 represent subscriber unitscoupled to a common coaxial transmission medium interconnecting thenetworks. The present invention does not assume a particular modulationsystem. Representative modulation systems include QAM and OFDM.

FIG. 2 depicts further details of hub 102. In order to interact with thecommon transmission medium, hub 102 includes a baseband physical layerprocessor 202 and in some applications such as wireless or cable, aradio converter 204. Baseband physical layer processor 202 includeshardware for implementing error correction coding, and any particularmodulation scheme employed such as OFDM or QAM. It is understood thatbaseband physical layer processor 202 includes hardware and software tosupport multiple upstream receivers and at least one downstreamtransmitter.. For transmission, radio converter 204 converts thebaseband output of baseband physical layer processor 202 to a selectedfrequency for transmission. For reception, radio converter 204 convertsa signal received at a selected reception frequency to baseband forinput to baseband physical layer processor 202. Again, it is understoodthat radio converter 204 includes hardware and software to supportmultiple upstream receivers and at least one downstream transmitter.Further exemplary detail of these two stages is discussed with referenceto FIG. 5.

A MAC processor 206 is responsible for multi-access control processing.MAC processor 206 receives and transmits IP packets to other componentsof hub 102. MAC processor 206 packages the IP data from the transmitpriority processor 216 within the packet format specified by theoperative MAC (medium access control) protocol. MAC processor 206extracts IP data from MAC packets received from baseband physical layerprocessor 202 and forms the IP packets transmitted on the other end ofthe link (CPEs). Some of the MAC packets received by MAC processor 206include access requests from CPEs 104. These access requests areforwarded to a bandwidth management processor 210.

In response to the access requests, a bandwidth management processor 210allocates available upstream bandwidth among CPEs 104. Any schedulingtechnique may be used according to the present invention. Oneconsideration in assigning center-frequency is channel quality availableat different center-frequencies taking into account signal to noiseratio and/or signal to noise-plus-interference ratio. The bandwidthmanagement processor 210 forwards assignments of frequency, data rate,and transmission frame to MAC processor 206 for inclusion in MAC packetsto be transmitted downstream. These assignments of center-frequency,data rate, and transmission frame provide the CPEs the informationregarding the time-frequency division of the upstream medium. Thisinformation is referred to as the MAP.

This MAP information is also forwarded to the radio link supervisionprocessor 208. The radio link supervisor 208 partitions the basebandphysical layer processor 202 and the radio converter 204 for properreception of the upstream according to the MAP information. Theoperation of bandwidth management processor 210 and radio linksupervision processor 208 is highly related. They may operate as eitherindependent or integrated software packages on the same computer system.

An IP router 212 exchanges IP packets with backbone class IP router 106via a Sonet ring 214. IP router 212 receives the IP packets from the MACprocessor 206. IP packets to be transmitted out over network 100 areprioritized by a transmit priority processor 216. For example, voicepackets and other real-time data are given a higher priority than otherkinds of data. Priority processor 216 queues up IP packets to betransmitted and forwards them to MAC processor 206 in order of priority.

FIG. 3 depicts a representative CPE 104 as an example of a datacommunications device in the network of FIG. 1 according to oneembodiment of the present invention. A video conference center 302, aPBX 304, and an Enterprise LAN 306 are representative data sources anddestinations. An IP router 308 is connected to Enterprise LAN 306, toPBX 304 via a TDM to IP interface 310, and to video conference interface302 via a video over IP interface 312. A radio converter 314 and abaseband physical layer processor 316 essentially mirror the similarlynamed components of hub 102. A radio converter 314 and a basebandphysical layer processor 316 include hardware and software to support atleast one downstream receiver and at least two upstream transmitters ora single upstream transmitter capable of varying its data rate.

A MAC processor 318 operates to assemble and dissemble packetsconforming to the operant MAC protocol. Much of the data extracted fromthe received MAC packets is in the form of IP packets which areforwarded to IP router 308. Some of the extracted data includes the MAPwhich carries instructions assigning transmission center-frequencies,data rates and frame times. These instructions are forwarded to a radiolink supervision processor 320. Radio link supervision processor 320controls the data rate, transmission times and center-frequencies ofoperation for baseband physical layer processor 316 and radio converter314.

A queue monitor 322 originates requests for access to the commontransmission medium. These access requests are forwarded to MACprocessor 318 for forwarding to hub 102. The requests include the amountand priority of information to be transmitted. IP packets to betransmitted are forwarded to MAC processor 318 from transmit priorityprocessor 324. Transmit priority processor 324 receives packets from IProuter 308 that are to be directed to hub 102 and queues them in orderof priority. Again, voice and other real-time traffic is given higherpriority. Transmit priority processor 324 also indicates when data is tobe transmitted and the amount of data to be transmitted to queue monitor322. It is in response to these inputs that queue monitor 322 generatesaccess requests.

FIG. 4A depicts a MAP with frame, data rate and center-frequencyassignments according to one embodiment of the present invention.According to the present invention, the spectrum available fordownstream communications is divisible in both the frequency and timedomains. FIG. 4A shows a series of frames in the time domain. A frame ishere understood to be a unit of time for which access to the commontransmission medium may be assigned to one or more CPEs 104. A requestaccess (RA) frame 402 is where individual CPEs may request access to thecommon transmission medium. Any known MAC scheme may be used to controlaccess to the medium in this frame such as CSMA, CSMA/CD, etc. If RAframe 402 includes an OFDM burst, access contention during RA frame 402may be ameliorated by assigning different groups of OFDM tones for useby different CPEs 104. This technique is explained in greater detail inthe U.S. patent application entitled MEDIUM ACCESS CONTROL PROTOCOL FOROFDM WIRELESS NETWORKS (Attorney Docket No. 018543-000300) filed on Feb.6, 1998. This application is assigned to the assignees of the presentapplication and its contents are herein incorporated by reference.

In the illustrated example, each CPE 104 may transmit upstream during agiven frame at either a 2 Mbps data rate, a 30 Mbps data rate, or not atall. The present invention is, however, not restricted to any particulardata rate, or number of possible data rates, or mixtures of data ratesin a frame. In an A frame 404, 15 CPEs 1-15 are scheduled to transmit,each transmitting at 2 Mbps at differing center-frequencies. In a Bframe 406, a different set of CPEs 2, 5, 6, 7, 9, 12, 14, 15, 17, 20,21, 22, 24, 26, and 30 are scheduled to transmit. In a C frame 408, theentire upstream spectrum is reserved for a single CPE 3 which transmitsat 30 Mbps. In a D frame 410, the upstream spectrum is again dividedamong 15 CPEs 1, 4, 7, 8, 10, 13, 16, 19, 21, 22, 25, 27, 29, 30, and32. In an E frame 412, a single CPE 9 occupies the entire upstreamspectrum. Thus, many CPEs may simultaneously transmit as low data ratesources or one CPE may transmit at a high data rate. The fluctuations ofnetwork traffic are typically such that demand for high data ratetransmission is episodic meaning that intermittent high information ratesources may be serviced adequately without compromising the needs of lowinformation rate sources. Assigning frames such as in FIG. 4A is done bybandwidth management processor 210.

In a preferred embodiment, the duration of the 30 Mbps frames is 267 usand each such frame holds a 1000 byte MAC layer packet. The duration ofthe 2 Mbps frames is 256 us and each CPE transmitting in such a frametransmits a 64 byte MAC layer packet. In an alternative embodiment,frame length is the same for both data rates. Preferably, downstreamcommunications do not share the spectrum employed for upstreamcommunications. However, the downstream communication may be multiplexedin the time domain with the upstream communication. Frames or frequencyslots within frames may then be allocated to downstream transmission.

In another preferred embodiment, each CPE 104 may transmit upstreamduring a given frame at either a 2 Mbps data rate or a 26 Mbps datarate, or not at all. However, the MAP assigns the same number ofdistinct data rate slots for every frame. This is shown in Fig, 4B,where each frame consists of two 2 Mbps frequency slots and one 26 Mbpsfrequency slot. This MAP construction simplifies the baseband physicallayer processor 202 and 316, along with the radio converter 204 and 314.In an A frame 604, 2 CPEs 1-2 are scheduled to transmit, eachtransmitting at 2 Mbps at differing center-frequencies. In this same Aframe, CPE 3 is scheduled to transmit at 26 Mbps data rate. In a B frame406, CPEs 1 and 3 are scheduled to transmit at 2 Mbps while CPE 4transmits at 26 Mbps. Frames C,D and E are used by other CPEs. Note thatCPE 1, by use of the MAP, has been allocated a constant data ratechannel of 2 Mbps. This MAP assignment is done by bandwidth managementprocessor 210.

FIG. 5 depicts details of baseband physical processor 202 and radioconverter 204 of hub 102. These details are presented for a QAMapplication, although the present invention is not limited to anyparticular modulation system. A single downstream system 502 isdepicted. Bits corresponding to MAC packet contents are received by bitsto symbol converter 504 and mapped to appropriate positions on a QAMconstellation. An upconversion stage 506 converts the signal output ofbits-to-symbol converter 504 to the frequency allocated for downstreamtransmission. This frequency may be selected by a signal from radio linksupervision processor 208. An amplification and filter stage 508 thenoutputs the signal onto the common transmission medium. There may ofcourse be more than one such downstream system.

A series of upstream receiver systems 510 are provided. In oneembodiment, there are upstream receivers for each possible 2 Mbpschannel and a separate receiver for use in frames in which the entireupstream spectrum includes a single 30 Mbps channel. Alternatively,there may be a series of upstream receiver systems 510 with selectableor fully variable data rate. In another embodiment, the entire upstreamspectrum is digitized and processed appropriately for each frame.

Each depicted upstream receiver system includes a preamplification andfilter stage 512 for receiving a signal from the common transmissionmedium. A downconversion stage 514 converts the received signal tobaseband. Downconversion stage 514 sets the frequency to be receivedbased on frequency control input from radio link supervision processor208. An equalizer 516 seeks to correct for distortion in thetransmission medium. A symbol decision stage 518 estimates thetransmitted symbols based on the output of equalizer 516. Equalizer 516is preferably a decision feedback equalizer (DFE) and adapts in responseto the output of symbol decision stage 518. A symbol to bits conversionstage 520 then generates the contents of the MAC packets.

FIG. 6 depicts representative details of baseband physical layerprocessor 316 and radio converter 314 of CPEs 104. Again, the detailsare presented in the context of QAM. A downstream receiver system 602 isused to receive data from hub 102. A preamplification and filter stage604 extracts the signal from the common transmission medium. Adownconversion stage 606 converts the received signal to baseband. Thereception frequency may be controlled by a signal from radio linksupervision processor 320. An equalizer 608 corrects for channeldistortion in the transmission medium. A symbol decision stage 610recovers the transmitted symbols. Equalizer 608 is preferably a DFE thatadapts in response to the output of symbol decision stage 610. A symbolto bit conversion stage 612 then converts the received symbols to theMAC packet data.

Two upstream transmitter systems 614 are depicted, one for the 2 Mbpstransmission data rate and one for 30 Mbps. Components may be sharedbetween the two systems. In an alternative embodiment, a singletransmitter system with selectable or even fully variable data rate isused.

In the depicted system, a switch 616 selects which bandwidth is to beused during a particular frame. MAC packet data is sent to theappropriate upstream transmitter system based on the setting of switch616. A bit to symbol conversion stage 618 converts the MAC packet datato QAM symbols. An upconversion stage 620 sets the transmissionfrequency based on input from radio link supervision processor 320. Anamplification and filter stage 622 prepares the signal for transmissionvia the common transmission medium.

The multirate upstream model provided by the present invention provideshigh quality service to both low information rate and high informationrate sources while maximizing spectral efficiency. Also, latency isminimized for real-time traffic such as voice and video conference data.

It is understood that the examples and embodiments described herein arefor illustrative purposes only and that various modifications or changesin light thereof will be suggested to persons skilled in the art and areto be included within the spirit and purview of this application andscope of the appended claims. All publications, patents, and patentapplications cited herein are hereby incorporated by reference.

1. (canceled).
 2. In a digital communications network comprising aplurality of data communications devices transmitting via a commontransmission medium and a hub receiving signals from said datacommunications devices via said common transmission medium, a methodcomprising: receiving access request messages from requesting datacommunication devices, said access request messages requesting access tosaid common transmission medium; allocating access to said commontransmission medium in both the frequency and time domain among saidrequesting data communication devices; and transmitting from said hub tosaid requesting access devices, instructions for each requesting accessdevice to transmit at particular times and frequencies, and atparticular data rates chosen in accordance with allocations by saidbandwidth manager.
 3. The method of claim 1 wherein said commontransmission medium comprises a wireless medium.
 4. The method of claim1 wherein said common transmission medium comprises a wired medium. 5.The method of claim 1 wherein said link supervisor comprises a radiolink supervisor.
 6. In a data communication network, a methodcomprising: transmitting requests at a bandwidth manager for access to acommon transmission medium to a hub; receiving at a link supervisor,medium access instructions from said hub, said medium accessinstructions specifying data rate, transmission time, and transmissionfrequency for transmissions to said hub; and controlling at the linksupervisor, transmission of information via said common transmissionmedium in accordance with said specified data rate, transmission time,and transmission frequency.
 7. The method of claim 6 wherein said commontransmission medium comprises a wired medium.
 8. The method of claim 6wherein said common transmission medium comprises a wireless medium. 9.The method of claim 8 further comprising communicating at selectabledata rates with at least two downstream radios.
 10. The method of claim6 wherein said link supervisor comprises a radio link supervisor.
 11. Adata communications device for use in a network, said datacommunications device comprising: means for transmitting requests at abandwidth manager for access to a common transmission medium to a hub;means for receiving at a link supervisor, medium access instructionsfrom said hub, said medium access instructions specifying data rate,transmission time, and transmission frequency for transmissions to saidhub; and means for controlling at the link supervisor, transmission ofinformation via said common transmission medium in accordance with saidspecified data rate, transmission time, and transmission frequency. 12.The device of claim 11 wherein said common transmission medium comprisesa wired medium.
 13. The device of claim 11 wherein said commontransmission medium comprises a wireless medium.
 14. The device of claim13 further comprising communicating at selectable data rates with atleast two downstream radios.
 15. The device of claim 11 wherein saidlink supervisor comprises a radio link supervisor.